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January 15, 2015

Mobile eavesdropping via SS7 and first reaction from telecoms

Mobile network operators and manufacturers finally said some words about vulnerabilities in the SS7 technology that allow an intruder to perform subscriber’s tracking, conversation tapping and other serious attacks. We reported some of these vulnerabilities and attack schemes in May 2014 at Positive Hack Days IV as well as here in our blog.

In December 2014, these SS7 threats were brought to public attention again, at the Chaos Communication Congress in Hamburg, where German researchers showed some new ways to intercept and decrypt mobile phone calls using SS7. The research have included more than 20 networks worldwide, including T-Mobile in the United States.
Meanwhile, the Washington Post reports that GSMA did not respond to queries seeking comment about the vulnerabilities in question. For the Post’s article in August on location tracking systems that use SS7, GSMA officials acknowledged problems with the network and said it was due to be replaced over the next decade because of a growing list of security and technical issues.

The reply from T-Mobile was more abstract: “T-Mobile remains vigilant in our work with other mobile operators, vendors and standards bodies to promote measures that can detect and prevent these attacks."

Huawei has obtained the vulnerability information from open channels and launched technical analysis.

Again, not too much said. But it’s better that nothing, considering the fact that SS7 problem is not new: it’s traced back to the seventies of the last century. In the early two thousands SIGTRAN specification was developed; it allowed transferring SS7 messages over IP networks. Security flaws of upper levels of SS7 protocols were still presented. The telecom engineers had been alerting that subscriber locating and fraud schemes using SS7 are possible, since 2001.

For obvious reasons, providers didn't want the public to know about these vulnerabilities. However, it's believed that law enforcement agencies used SS7 vulnerabilities to spy on mobile networks for years. In 2014, it was found out that there are private companies providing a whole range of the above-mentioned services to anyone who wants. For example, this is how the SkyLock service provided by the American company Verint works:

Washington Post notes that Verint do not use their capabilities against American and Israeli citizens, "but several similar systems, marketed in recent years by companies based in Switzerland, Ukraine and elsewhere, likely are free of such limitations".

Data presented in this report were gathered by Positive Technologies experts in 2013 and 2014 during consulting on security analysis for several large mobile operators and are supported by practical researches of detected vulnerabilities and features of the SS7 network.

The testing revealed that even the top 10 telecom companies are vulnerable to these attacks. Moreover, there are known cases of performance of such attacks on the international level, including discovering a subscriber's location and tapping conversations from other countries.

Common features of these attacks:

The intruder doesn't need sophisticated equipment. We used a common computer with OS Linux and SDK for generating SS7 packets, which is publicly available on the web.

Upon performing one attack using SS7 commands, the intruder is able to perform the rest attacks by using the same methods. For instance, if the intruder managed to determine a subscriber's location, only one step left for SMS interception, transfer of funds etc.

Attacks are based on legitimate SS7 messages: you cannot just filter messages, because it may have negative influence over the whole service. An alternative way to solve the problem is presented in the final clause of this research.